custom url rewrite not working with forum

Hello,

I've just installed a forum onto my drigg site and i see that url's for the topics are "node/$nid".
I tried editing the custom_url_rewrite_function.php file by adding the following:

if (preg_match('|^node/(.*)|', $path, $matches)) {
        $nid = $matches[1];
        $res=drigg_settings_lookup_node_type_by_nid($nid);
        if($res=="forum"){
          $res=urlencode($res);
          return("/forum/".$nid);
        }
    }


function drigg_settings_lookup_node_type_by_nid($nid){
  static $cache;
  if(!$cache[$nid]){
    $res=db_result(db_query("SELECT type FROM {node} WHERE nid =%d",$nid));
    $cache[$nid]=$res;
    #drupal_set_message("HERE: SELECT type FROM {node} WHERE nid =$nid: $res");

  }
  return $cache[$nid];
}

But it doesn't seem to do anything. Any suggestions?